The invention relates to electronic magnetometers and compasses.
An inexpensive, electronic magnetometer of simple construction is described in U.S. Pat. No. 4,916,821, which is incorporated by reference. The electronic magnetometer described in that patent includes a pair of flux-concentrating concentrating elements arranged in an overlapping fashion. The flux-concentrating elements are vibrated such that they rattle randomly or non-coherently against each other. By non-coherent, it is meant that energy is dispersed over numerous mechanical frequencies. This causes the magnetic field in the region of the juncture of the flux-concentrating elements to vary non-coherently as well. Consequently, current induced in a pickup coil surrounding the juncture varies in a non-coherent fashion. The induced current drives a speaker which, because the current varies non-coherently, produces a hiss. Oscillator leakage currents produce a slight whine audible through the hiss. Except at magnetic null, the amplitude of the hiss swamps the leakage whine. The ear's capacity to ignore the whine permits nulling to less than 10 seconds of arc.
The electronic magnetometer is swept through a horizontal arc to locate the east-west null in the Earth 's magnetic field. When the flux-concentrating elements are aligned along the null, flux through them falls to zero. Accordingly, the non-coherent current induced in the pickup coil falls to zero and the hiss disappears, indicating east-west alignment.
It has been found through experience that the nulling sensitivity and accuracy of the magnetometer of U.S. Pat. No. 4,916,821 declines as the flux-concentrating elements are tilted away from level with the ground, since one element tip lies on top of the other element tip, and tilting the device above or below the horizon lightens the pressure of the upper element tip on the lower element tip. Furthermore, freedom of motion is required for the flux-concentrating elements to vibrate chaotically, and this freedom permits them to vibrate slightly in and out of alignment with each other. As a result, nulling accuracy is decreased.
The device can also be used as an electronic compass.